[grahame]

Thus, unlike with the F teleconverter, you don't have to change the focus setting on the lens to gain access to the full range of focus settings.

But actually when I used the AFA 1.7x in the field, with DA 300 or FA 300, I found by pre-focusing the lens to the area, the adapter focuses faster than DA300+ 1.4 teleconverter.
300+ 1.7X works really well when I was shoot swan in the pond, landing or taking off, they are usually in that area.
But I do had problem when a bird showed up suddenly and I had to manual focus the lens and then press shutter to start AF on adapter.

[snostorm]

It's specifically better than the F 1.7x teleconverter in this area because rather than having an AF mechanism of its own, the DA 1.4x lets the camera directly control the lens's screwdrive or SDM motor. Thus, unlike with the F teleconverter, you don't have to change the focus setting on the lens to gain access to the full range of focus settings. On top of that, the extra half stop of light allows for faster PDAF operation.

Having an AF mechanism of its own can also be an advantage. I use the F 1.7x AFA quite a bit with AF lenses -- because of the limited range of focus and the speed of locking focus within that range. For me, the AFA works as the most effective focus limiter I've used (much easier to use than the one on the FA* 300/2.8, for ex). I can use AF to make tiny focus adjustments for static subjects (like perching birds) without having to worry that the lens might go into a long lock to lock focus hunt. Even if it does lose fine focus and hunt, the process with the limited focus range only takes a fraction of a second, and I'm back on track.

I even use the AFA with my dedicated macro lenses so I can use AF shooting macro, which is usually thought of as impractical. The focus range with the AFA at macro distances is tiny, and even a lock to lock focus hunt only moves the focus point a few mm, if even that. The added magnification is a bonus.

Also, the AFA does convert f-stop in the camera for exif, and because it does not pass a FL from the lens, it requires that you set FL up when mounted (and holds this FL info from the last time I used the AFA), so FL to match SR is not the problem it is with a 3rd party TC. If you use a lot of different lenses with it, then you must manually change the FL for SR, if you use the same lens, it's essentially automatic.

I guess advantages/disadvantages pretty much depends on one's perspective.

Scott

[normhead]

Also, the 1.7 on my A-400 doesn't let enough light through to the camera to AF properly, even for focus confirmation.. The camera will mislead you. You have to ignore the focus confirm.

The AF the on 1.7 woks great on the 200 ƒ2.8, acceptably well on the DA 60-250 ƒ4. Not on the A-400 5.6. It was clearly designed for ƒ 2.8 lenses, with ƒ4 being the upper limit.

[UncleVanya]

Also, the 1.7 on my A-400 doesn't let enough light through to the camera to AF properly, even for focus confirmation.. The camera will mislead you. You have to ignore the focus confirm.

The AF the on 1.7 woks great on the 200 ƒ2.8, acceptably well on the DA 60-250 ƒ4. Not on the A-400 5.6. It was clearly designed for ƒ 2.8 lenses, with ƒ4 being the upper limit.

Not to gainsay you too much but my AF 1.7x copy worked great on an FA 300 f/4.5 as well as an older M series 80-200 f/4.5 - it also worked in combination with the 1.4x-S A series adapter on the FA 300 but I was shooting the moon so your mileage may vary.

[normhead]

Well then, I'll conclude ƒ4.5 is the upper limit. I couldn't do that test. I don't have an ƒ4.5 lens. I am sure it's worthless at 5.6. That could be quite useful information if you have a Sigma 500, 4.5. How about AF at 850mm?

[Adam]

most effective focus limiter I've used

That's a great application- never thought of it that way!

[UncleVanya]

Well then, I'll conclude ƒ4.5 is the upper limit. I couldn't do that test. I don't have an ƒ4.5 lens. I am sure it's worthless at 5.6. That could be quite useful information if you have a Sigma 500, 4.5. How about AF at 850mm?

I sold my 1.7x and I am afraid the only 500 I ever owned was the takumar.

[grahame]

I'll conclude ƒ4.5 is the upper limit. I couldn't do that test.

Yes, I can confirm that. AFA1.7x works great with FA 300/4.5 even at not so great light. I took some nice swan photos in the evening, ISO 1600, F9, shutter speed 1/200. focusing was fast and accurate, without much hunting.
I will guess at good light, F5.6 lens will be fine.

[normhead]

Yes, I can confirm that. AFA1.7x works great with FA 300/4.5 even at not so great light. I took some nice swan photos in the evening, ISO 1600, F9, shutter speed 1/200. focusing was fast and accurate, without much hunting.
I will guess at good light, F5.6 lens will be fine.

The last time I tried the A-400 with the 1.7 at distance the results were miserable, as in 30 images, not one useable, not one even remotely in focus. I now, just manually adjust the lens. But that was at 100 meters. I do have some closer images that have worked.

[UncleVanya]

Another member tried with the A600 and had dismal results also. Perhaps the longer focal length plus the slower aperture collectively contribute?

[fwcetus]

most effective focus limiter I've used

That's a great application- never thought of it that way!

Adam, if you've ever been autofocusing with a lens such as one of the 55-300/4-5.8 zooms (or the Tokina AT-X 80-400/4.5-5.6), and had it go full-zoom-travel on you a couple of times, but then quickly added the F 1.7X AFA, you would have been ~instantly~ very aware ~and~ impressed by the dramatic improvement in hunting (or lack thereof).

[Disclaimer # 1 -- You need a lot of light to use the AFA with these sort of zooms, especially at the long end).]

[Disclaimer # 2 -- This post in no way should be taken as being overly critical of the DA 55-300/4-5.8, the best consumer tele zoom ~evah~.]

[Afterthought -- it's just too bad that more such lenses didn't already come with focus limiters...]

[snostorm]

Well then, I'll conclude ƒ4.5 is the upper limit. I couldn't do that test. I don't have an ƒ4.5 lens. I am sure it's worthless at 5.6. That could be quite useful information if you have a Sigma 500, 4.5. How about AF at 850mm?

Hi Norm,

f 4.5 is probably a good estimation for the upper limit of max aperture for using the 1.7x AFA. it gives an effective max aperture of f7.7, which on paper is very slow, but my experience is that the FA* 300/4.5 + the AFA will AF effectively in everything down to moderate overcast daylight conditions -- so it's very useful for me, and this is my goto everyday birding lens combo. It's only a half stop slower than most xx-500 zooms and the size/weight advantages are significant. I'll use a 300/2.8 + 1.4x and the 1.7x AFA to get more reach (714mm f6.7). With these lens combos, I really don't want/need anything longer in a super tele prime, mainly because I shoot close for the most part -- 10-15 ft, and the longer prices usually have a minimum focus distance of 13 ft or more. I passed on a very nice deal on a rare Sigma MF 500/4.5 from Kerrick James for this very reason.

With an F5.6 lens, it takes pretty bright direct sunlight, and even then AF not very reliable, so I don't even try any more. My rule of thumb for AF with TCs with Pentax bodies is that the effective max aperture needs to be faster than f8 for AF to be anywhere close to actually useful for me.

As Pentax has evolved it's AF sensor sensitivity, the absolute limit for any AF capability has moved beyond f8, but for AF to be actually useful for me, I still consider faster than f8 as my guideline for the effective max aperture (max aperture of the lens * the magnification of the TC) for TC use with AF.

Scott